Question

Why do we need a step-up transformer for long-distance transmission of electric power?

Answer 1

Electric power is transmitted over long distances through overhead wires, which have resistance. The power transmitted is given by P = V × I. If the voltage is low, the current becomes very large for the same power. The heat loss in the transmission wires is I²R, so a large current causes a huge energy loss as heat. A step-up transformer increases voltage and decreases current while keeping power the same. This reduces the I²R loss greatly. Therefore, a step-up transformer is needed at the generating station before transmitting power over long distances.